Early changes in blood chemistry and the electroencephalogram were monitored during the first three hours after initiating the medium chain triglyceride (MCT) diet in nine children with intractable atypical absence seizures. Serum glucose, insulin, triglycerides, cholesterol, free fatty acids, ketone bodies concentrations, and venous pH were assayed before and at timed intervals after MCT oil was administered orally. The concentration of serum ketones rose progressively over three hours, β-hydroxybutyrate proportionately higher than acetoacetate. A statistically significant decrease in the group mean number of epileptiform discharges occurred following MCT therapy. Seizure frequency decreased by more than 50 percent in two-thirds of the children during the 10 week treatment period.